1. Field of the Invention
This invention relates to a radiotelephone apparatus which is employed as a portable telephone or a car telephone.
2. Description of the Related Prior Art
There has been proposed a radiotelephone apparatus in which, for transmission and reception of speech signals, the speech signal input from a mouthpiece is transmitted on one radio link, and the party's speech signal transmitted on the other radio link is received and output as the party's voice from an earpiece.
Among these radiotelephone apparatus are portable or car telephones of, for example, Cellular Mobile Telephones in which the speech signals are transmitted and received via the base station.
As an example of such radiotelephone apparatus, there is proposed an apparatus which is comprised of a main body operating as a so-called cradle section, and a so-called handset section which is detachably mounted on an outer casing of the main body.
The handset contains a microphone device for converting the speech signal into the electrical signal and a speaker device for converting the electrical signal into the received speech signal, and is so constructed that the user of the apparatus may put the microphone device and the speaker device near his or her mouth and near his or her ear, respectively.
The main body of the apparatus includes an outer casing, and on the outer side of which the handset is adapted to be retained detachably.
The main body of the apparatus also includes a transmitting circuit for processing electrical signals from the microphone device of the handset over a signal cable in predetermined manner and transmitting the processed signal as radio wave signals over an antenna together with predetermined signals for identifying the destination of transmission, and a receiving circuit for receiving radio wave signals transmitted from the base station over the antenna, processing the received radio wave signals in a predetermined manner to the electrical signal and driving the speaker device of the handset with the processed signals over the signal cable.
Meanwhile, the main body of the apparatus also includes a radio frequency signal amplifying circuit for amplifying the radio frequency signals to be transmitted.
This radio frequency signal amplifying circuit is provided with a power amplifying device which emit heat during operation If heated to higher than a predetermined temperature, the power amplifying device may become unable to perform a prescribed operation.
For this reason, with the above described conventional radiotelephone apparatus, the heat generated from the power amplifying device is radiated to the outside of the main body to prevent the output circuit and the interior of the outer casing from being heated to higher than predetermined temperatures.
In one embodiment, in a radiotelephone apparatus, a power amplifying device is mounted on the heat sink in the thermally conductive relation and the heat generated in the interior of the radio&telephone apparatus is radiated by the thermally conductive heat sink fins cooled by natural air flow.
However, this type of heat radiating device results in increased size and weight of the radiotelephone apparatus.
Hence, when the radiotelephone apparatus is mounted in the vicinity of the driver s seat in a vehicle, the oversized radiotelephone apparatus impedes other operations in the vehicle.
Meanwhile, when the apparatus is held by hand and used outdoors, for example, the increased size or weight of the apparatus is inconvenient for transportation.
Furthermore, when the apparatus is initially operated in so called hands-free operation with the handset left on the main body of the apparatus and then switched to the handset conversation, it arises an uncomfortable feeling in using the handset if surface of the handset is heated by the leaked heat from the main body which contains a heated power amplifying device.
Meanwhile, there is known a measurement instrument in which heat sink fins and a cooling fan device are provided in the casing of the instrument. This cooling system is so designed that outside air is sucked from an air intake window provided on the back panel of the outer casing to direct the air to the heat sink fins on which heated elements are mounted and the air is discharged from the inside of the outer casing via air outlet windows provided on the side of the outer casing.
However, dust and dirt contained in the air sucked at the air intake window tend to become affixed to the intake window, printed circuit board, and to various components in the outer casing.
If dust and dirt are heaped on the window it may cause degradation in air cooling performance. And if dust and dirt are heaped on the printed circuit board, or other components in the outer casing, there arises the risk that the components may become unable to operate or the electrically conductive patterns on the printed circuit board or electrical components mounted thereon may be shorted by the dust and dirt electrically and mechanically.
Also, since the dust and dirt heaped on the heat sink tend to impede heat radiation from the heat sink, the measuring instruments are usually provided in measuring or test chambers where a lesser amount of dust and dirt is produced.
Such concept of cooling the measuring instruments cannot desirably by applied to car telephones or portable telephones likely to be used outdoors since an exceedingly large amount of dust and dirt is entrained on outside are and, on windy days above all, the amount of sand and or dust and dirt entrained in outside air is exceedingly increased.